Power Line Communication (PLC) is one of the technologies used for automatic meter reading, for example. Both one-way and two-way systems have been successfully used for decades. Interest in this application has grown substantially in recent history because utility companies have an interest in obtaining fresh data from all metered points in order to better control and operate the utility grid. PLC is one of the technologies being used in Advanced Metering Infrastructure (AMI) systems.
A PLC carrier repeating station is a facility at which a PLC signal on a power line is refreshed. The signal is filtered out from the power line, demodulated and modulated, and then re-injected onto the power line again. Since PLC signals can carry long distances (several 100 kilometers), such facilities typically exist on very long power lines using PLC equipment.
In a one-way system, readings “bubble up” from end devices (such as meters), through the communication infrastructure, to a “master station” which publishes the readings. A one-way system might be lower-cost than a two-way system, but also is difficult to reconfigure should the operating environment change.
In a two-way system, both outbound and inbound traffic is supported. Commands can be broadcast from a master station (outbound) to end devices, such as meters, that may be used for control and reconfiguration of the network, to obtain readings, to convey messages, etc. The device at the end of the network may then respond (inbound) with a message that carries the desired value. Outbound messages injected at a utility substation will propagate to all points downstream. This type of broadcast allows the communication system to simultaneously reach many thousands of devices. Control functions may include monitoring health of the system and commanding power shedding to nodes that have been previously identified as candidates for load shed. PLC also may be a component of a Smart Grid.
The power line channel is very hostile. Channel characteristics and parameters vary with frequency, location, time and the type of equipment connected to it. The lower frequency regions from 10 kHz to 200 kHz are especially susceptible to interference. Furthermore, the power line is a very frequency selective channel. Besides background noise, it is subject to impulsive noise often occurring at 50/60Hz, and narrowband interference and group delays up to several hundred microseconds.
OFDM is a modulation technique that can efficiently utilize this limited low frequency bandwidth, and thereby allows the use of advanced channel coding techniques. This combination facilitates a very robust communication over a power line channel.
On Sep. 30, 2010, the IEEE's 1901 Broadband Powerline Standard was approved and HomePlug AV, as baseline technology for the FFT-OFDM PHY within the standard, is now ratified and validated as an international standard. The HomePlug Powerline Alliance is a certifying body for IEEE 1901 products. The three major specifications published by HomePlug (HomePlug AV, HomePlug Green PHY and HomePlug AV2) are interoperable and compliant.
Another set of open standards has been developed for power line communication (PLC) at the request of Electricite Reseau Distribution France (ERDF), a wholly owned subsidiary of the EDF (Electricite de France) Group. The set of standards include “PLC G3 Physical Layer Specification,” undated, ERDF; and “PLC G3 MAC Layer Specification,” undated, ERDF. These standards are intended to facilitate the implementation of an automatic meter-management (AMM) infrastructure in France; however, PLC using these standards or similar technology may be used by power utilities worldwide.
The G3 standards promote Interoperability and coexists with IEC 61334, IEEE® P1901, and ITU G.hn systems. 10 kHz to 490 kHz operation complies with FCC, CENELEC, and ARIB. CENELEC is the European Committee for Electrotechnical Standardization and is responsible for standardization in the electro technical engineering field. ARIB is a Japanese standards organization.
Generally speaking, prior to transmitting a signal across power lines or wires, a PLC device may attempt to detect whether a given communication or access channel (e.g., frequency band) is currently in use. Channel access may be accomplished, for example, by using the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) mechanism with a random backoff time.